Yemeni forces opened fire Tuesday on protesters in Sanaa, killing 12 and wounding over 70, a medical official said. Firefights between troops loyal to Yemen's president and rival forces on Monday killed several people, including eight supporters of a powerful tribal chief who defected to the opposition in March, the AP reported.

Soldiers from the Republican Guard, a loyalist unit led by President Ali Saleh's son Ahmed, detained four female protesters who were ahead of the main demonstration, said activist Habib al-Uraiqi.

Demonstrations were held in other parts of Yemen, including the southern cities of Aden and Taez. The protesters called for Saleh to be put on trial for killing demonstrators.